a) Field of the Invention
The invention is directed to a device for the deflection of a light bundle generated by a light source, wherein this device has a nonmechanical deflection device in which the light bundle enters and exits at a different angle determined by a controlling variable, which angle depends on the wavelength of every light component in the light bundle. The invention is further directed to a use of this device and to a video system in which this device is used for deflection.
b) Description of the Related Art
Devices for the deflection of a light bundle are known particularly from laser printers. In laser printers, a light-sensitive roller or drum is written on by a light beam which is electrically charged at the locations illuminated in this way, so that toner material is deposited at these locations and is subsequently transferred to paper. The writing light beam is deflected line by line for this purpose. Electro-optic and acousto-optic deflection devices have proven especially economical for this purpose and also enable high deflection frequencies up to the gigahertz range.
In video technology, in order to display color video images as is known, for example, from DE 43 24 849 C2, a light bundle is also deflected, although in two directions. The deflected light bundle illuminates sequentially on a screen the individual image points of the video image to be displayed.
In order to show color video images, the laser light bundle is usually composed of three light bundles of different colors. However, this combined light bundle cannot easily be deflected by means of an acousto-optic deflector as is known from printing technology, because its deflection angle is wavelength-dependent, which results in a separation of colors of the total light bundle.
Therefore, mechanical deflection systems are used as a rule in video technique. In this connection, line deflection, for which high deflection frequencies are required above all, is usually carried out by a polygon mirror which has different mirror faces arranged as the sides of a polygon and which is operated at rotational frequencies in the kilohertz range. With 25 mirror facets and a rotating frequency of the polygon mirror of 1.3 kHz, a horizontal deflection frequency of 32.5 kHz is achieved.
Costly technology is required to provide polygon mirrors with high rates of rotation and the required precision accompanied by high dependability and long life. In general, the cost of such mirrors is very high and they are therefore poorly suited to mass production.
Another basic disadvantage consists in the limited deflection speed. The technical limit is currently approximately 32 kHz deflection frequency. For areas of application in the above-mentioned video technology when used for CAD in simulators or in electronic cinema, a multiple of this deflection speed is required. Such systems can be realized only at a high technical expenditure and it is to be expected that the costs for this purpose will multiply compared with conventional polygon mirrors.
On the other hand, nonmechanical deflection devices which make use of electronic, magnetic or acousto-optic effects, for example, or virtual gratings in accordance with DE 44 04 118 C2 are extremely expensive. However, because of their dispersion, i.e., the dependence of the deflection angle on the wavelength of the light bundle, they are generally not suitable for imaging color pictures. For the various possibilities of nonmechanical deflection devices, reference is had by way of example to the book "Der Laser in der Druckindustrie [The Laser in the Printing Industry"], W. Hulsbusch, Constance, Verlag W. Hulsbusch, 1990; Chapter 2.3.
However, it is proposed in U.S. Pat. No. 5,253,073 for the generation of light bundles of different colors which are combined to form a total light bundle to use pulsed lasers whose light pulses pass successively through an acousto-optic deflector which is used as a deflection device and which is then acted upon by different switching frequencies as controlling variables for the respective light pulse located in the deflector.
The switching speed of acousto-optic deflectors of this type depends, however, on the speed of sound in the acousto-optically active material and on the diameter of the light bundle. Because of the limitation due to the velocity of sound, switching speeds in the order of magnitude of several microseconds are achieved when quickly switching from one color to the other at the same deflection angle for the different frequency-dependent controlling variables in the so-called random access mode which is used in this case. This time period is not sufficient for fast changing of picture points according to conventional video standards.
The advantage of the high deflection speed made possible by acousto-optic deflectors with uniform deflection can therefore not be utilized, so that polygon mirrors and galvanometer mirrors must continue to be relied on for deflection of the light bundle for video systems of the type mentioned above.